android Activity 不显示状态栏

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    android:orientation="vertical">
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar1"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/AppTheme.PopupOverlay" />
    <android.support.design.widget.TabLayout android:id="@+id/tabLayout"
        android:layout_width="match_parent" android:layout_height="wrap_content" />
    <android.support.v4.view.ViewPager android:id="@+id/viewPager"
        android:layout_width="match_parent" android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</LinearLayout>

public class TabActivity extends AppCompatActivity  {
    private SectionsPagerAdapter mSectionsPagerAdapter;
    private ViewPager mViewPager;
    private TabLayout tabLayout;
    private List<String> mTitles = new ArrayList<String>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tab);
        tabLayout = (TabLayout) findViewById(R.id.tabLayout);
        mViewPager = (ViewPager) findViewById(R.id.viewPager);
        mTitles.add("TAB1");
        mTitles.add("TAB2");
        mTitles.add("TAB3");
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager(),mTitles);
        mViewPager.setAdapter(mSectionsPagerAdapter);
        tabLayout.setupWithViewPager(mViewPager);
    }
    public static class PlaceholderFragment extends Fragment {
        private static final String ARG_SECTION_NUMBER = "section_number";
        private static int pos=0;
        public PlaceholderFragment() {
        }
        public static PlaceholderFragment newInstance(int sectionNumber) {
            pos = sectionNumber;
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_tab, container, false);
            TextView textView = (TextView) rootView.findViewById(R.id.section_label);
            textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
            return rootView;
        }
    }
    public class SectionsPagerAdapter extends FragmentPagerAdapter {
        private List<String> titles;
        public SectionsPagerAdapter(FragmentManager fm,List<String> mTitles) {
            super(fm);
        }
        @Override
        public Fragment getItem(int position) {
            return PlaceholderFragment.newInstance(position);
        }
        @Override
        public int getCount() {
            return titles.size();
        }
        @Override
        public CharSequence getPageTitle(int position) {
            return titles.get(position);
        }
    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.scxn.demo.TabActivity$PlaceholderFragment">
    <TextView android:id="@+id/section_label" android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>